Intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing a diseased vessel, such as an artery, within the human body to determine the need for treatment, to guide the intervention, and/or to assess its effectiveness. An IVUS device including one or more ultrasound transducers is passed into the vessel and guided to the area to be imaged. The transducers emit ultrasonic energy in order to create an image of the vessel of interest. Ultrasonic waves are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. Echoes from the reflected waves are received by the transducer and passed along to an IVUS imaging system. The imaging system processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the device is placed.
There are two general types of IVUS devices in use today: rotational and solid-state (also known as synthetic aperture phased array). For a typical rotational IVUS device, a single ultrasound transducer element is located at the tip of a flexible driveshaft that spins inside a plastic sheath inserted into the vessel of interest. The transducer element is oriented such that the ultrasound beam propagates generally perpendicular to the axis of the device. The fluid-filled sheath protects the vessel tissue from the spinning transducer and driveshaft while permitting ultrasound signals to propagate from the transducer into the tissue and back. As the driveshaft rotates, the transducer is periodically excited with a high voltage pulse to emit a short burst of ultrasound. The same transducer then listens for the returning echoes reflected from various tissue structures. The IVUS imaging system assembles a two dimensional display of the vessel cross-section from a sequence of pulse/acquisition cycles occurring during a single revolution of the transducer.
In contrast, solid-state IVUS devices carry a transducer complex that includes an array of ultrasound transducers distributed around the circumference of the device connected to a set of transducer controllers. The transducer controllers select transducer sets for transmitting an ultrasound pulse and for receiving the echo signal. By stepping through a sequence of transmit-receive sets, the solid-state IVUS system can synthesize the effect of a mechanically scanned transducer element but without moving parts. Since there is no rotating mechanical element, the transducer array can be placed in direct contact with the blood and vessel tissue with minimal risk of vessel trauma. Furthermore, because there is no rotating element, the interface is simplified. The solid-state scanner can be wired directly to the imaging system with a simple electrical cable and a standard detachable electrical connector.
Innovations in IVUS catheters have resulted in dramatic improvements in sensitivity and resolution, thereby enhancing the quality of diagnostic data obtained. As the sensing instruments improve, the onus is placed on the imaging system and the associated processing methods to keep pace. This has coincided with the development of multi-modality systems that collect and process medical data from a plurality of different imaging, treatment, diagnostic, and sensing tools including angiography, intravascular ultrasound (IVUS), forward-looking IVUS (FL-IVUS), fractional flow reserve (FFR) determination, a coronary flow reserve (CFR) determination, optical coherence tomography (OCT), transesophageal echocardiography, and image-guided therapy.
The increased data and processing power available allows for greater refinement of the IVUS processing techniques. However, such improvements may drive the algorithms and processes to become increasingly application specific. Each variant of the process may be better suited for different diagnostic situations. Furthermore, while the IVUS imaging process may be adjusted to suit the imaging environment, this fine-tuning often places the burden on the user to understand and apply the correct adjustments. Surgical time is expensive, and system features that are complicated and time consuming may see infrequent use. Thus, while existing imaging systems have proved useful, there remains a need for user interface improvements that allow the operator greater control over the system without overwhelming the operator with options.